1. Technical Field
The present invention relates to fine patterning using exposure technologies, such as holography. Specifically, the invention relates to a method for aligning an exposure mask and an object to be exposed, and a method for manufacturing a thin film device substrate using the method.
2. Related Art
In recent years, Total Internal Reflection (TIR) holographic exposure technology has been a focus of attention as a patterning process for semiconductor devices. This exposure technology includes recording a desired pattern onto a holographic mask by using a holographic exposure system, and exposing a photoresist for a circuit pattern by irradiating a reconstructing beam onto the holographic mask.
In the recording, a recording laser beam is irradiated onto a mask pattern (former reticle) that corresponds to a pattern for a semiconductor device, producing a diffracted beam to be radiated onto a recording surface of a holographic mask. Meanwhile, a reference beam is irradiated onto the recording surface of the holographic mask from the opposite side of the holographic mask at a predetermined angle so as to interfere with the diffracted beam emitted from the original reticle. In this way, an interference pattern is produced and then recorded on the recording surface of the holographic mask.
In the exposing, an exposing beam, which is a reconstructing beam, is irradiated, from the opposite direction to that in the recording, onto the holographic mask that is placed on the same position as in the case of the original reticle so as to expose a photoresist together with a diffracted beam that reconstructs the original pattern on the photoresist. Generally, in the exposing, a substrate and a holographic mask are positioned appropriately by overlapping the alignment marks formed on the substrate, which is an object to be exposed, and the alignment marks formed on the holographic mask.
In the case where a patterning is done using a plurality of holographic masks, the alignment of a substrate and the holographic masks is generally done using a substrate on which alignment marks are respectively formed on the positions that correspond to each set of alignment marks formed on each of the plural holographic masks, as described in a document of related art, Symposium of Image Display (SID)03 Digest, P-40, pp.350-353.
Therefore, there is a problem that as many sets of alignment marks as holographic masks have to be placed on a substrate, requiring more alignment marks on a substrate in proportion to the increasing number of holographic masks to be used, which eventually requires a larger area on a substrate for forming alignment marks.
In the holographic exposure system, alignment marks to be placed on holographic masks need to be formed separately from device areas. Specifically, it is necessary to form alignment marks at an interval of about 5 mm from device areas and from alignment marks for other holographic masks (other layers), for the sake of accuracy of a manufacturing system (refer to FIGS. 11 and 12).
FIGS. 11A and 11B are two-dimensional diagrams schematically showing a first layer mask and a second layer mask, each being an original Cr mask (an former reticle) for forming a holographic mask. As shown in FIG. 11A, the first layer mask includes a first layer device area D1 in the center and a first layer alignment mark A1 on each corner. Meanwhile, as shown in FIG. 11B, the second layer mask includes a second layer device area D2 in the center and a second layer alignment mark A2 on each corner. The pattern of the alignment mark A1 and the pattern of the alignment mark A2 are different from each other.
FIGS. 12A and 12B are diagrams schematically showing procedures on the holographic mask (the second layer mask) for recording a device area and for recording alignment marks, respectively. As shown in FIG. 12A, in the recording of a device area, recording is done onto the holographic mask, with the four alignment marks A2 on the original Cr mask 2 closed with light shields, by an object beam passing through the device area D2 and a reference beam passing through a prism. Meanwhile, as shown in FIG. 12B, in the recording of alignment marks, recording is done onto the holographic mask, with the device area D2 closed with a light shield, by an object beam passing through the four alignment marks A2 on the original Cr mask 2. Here, on the resulting holographic mask, the alignment marks and the device area are placed at an interval of about 5 mm from each other. Further, although it is not shown in the drawings, in the case where more alignment marks for other layers are placed on the same mask with the first four alignment marks, each of the alignment marks is placed at an interval of about 5 mm from each other.
In the case of a combined exposure, the upper layer alignment marks are patterned overlappingly onto the lower layer alignment marks, making them unreusable for alignments in further exposures.